In a conventional pneumatic tire of the “tubeless” type (that is to say of the type without an inner tube), the radially internal face comprises an airtight layer (or more generally a layer that is impermeable to any inflation gas) which enables the pneumatic tire to be inflated and kept under pressure. Its sealing properties enable it to guarantee a relatively low rate of pressure loss, making it possible to keep the tire inflated, in the normal operating state, for a sufficient time, normally several weeks or several months. It also has the role of protecting the carcass reinforcement and more generally the rest of the tire from a risk of oxidation due to the diffusion of air coming from the internal space of the tire.
This role of airtight inner layer or “inner liner” is today fulfilled by compositions based on butyl rubber (isobutylene/isoprene copolymer), long renowned for their excellent sealing properties.
However, one well-known drawback of compositions based on butyl rubber or elastomer is that they have high hysteresis losses, furthermore over a wide temperature range, which drawback degrades the rolling resistance of pneumatic tires.
Reducing the hysteresis of these sealing inner layers and therefore, in fine, the fuel consumption of motor vehicles, is a general objective which current technology comes up against.
Document WO 2009/007064 by the Applicant companies discloses an inflatable article provided with a layer impermeable to inflation gases, in which the airtight layer has an elastomer composition comprising at least one thermoplastic styrene (TPS) elastomer and a platy filler, in which the volume content of the platy filler relative to the elastomer composition is greater than 5% (% by volume of the elastomer composition). Compared with a butyl rubber, the thermoplastic styrene elastomer has the major advantage, due to its thermoplastic nature, of being able to be worked as is in the molten (liquid) state, and consequently of offering a possibility of simplified processing; it has also proved compatible with the use of a platy filler in particularly high amounts, which makes it possible to improve the sealing compared with the solutions known from the prior art based on butyl rubber.
In the continuance of their research, the Applicant companies have discovered that a judicious choice of platy fillers also makes it possible to improve the sealing properties of the airtight layers based on a thermoplastic styrene (TPS) elastomer.
According to a first subject, the present invention relates to a similar inflatable article in which the elastomer composition comprises a platy filler having an equivalent diameter (DV(0.5)) of between 20 and 45 micrometers and a shape factor (F) greater than 65 with:
      F    =                            S          BET                          S          sphere                    =                        ρ          ⁢                                          ⁢                      S            BET                    ⁢                                    D              V                        ⁡                          (              0.5              )                                      6              ,in which:                SBET is the specific surface area of the platy filler measured by the BET method, in m2/g;        Ssphere is the specific surface area, in m2/g, of a sphere of identical equivalent diameter DV(0.5);        Dv(0.5) is the equivalent diameter in μm; and        ρ is the density of the platy filler in g/cm3.        
The invention particularly relates to inflatable articles made of rubber such as pneumatic tires, or inner tubes, especially inner tubes for a pneumatic tire.
The invention relates more particularly to the pneumatic tires intended to be fitted on motor vehicles of the passenger type, SUVs (Sport Utility Vehicles), two-wheel vehicles (especially motorcycles and bicycles), aircraft, or industrial vehicles chosen from vans, “heavy” vehicles, i.e. underground trains, buses, heavy road transport vehicles (lorries, tractors, trailers), off-road vehicles, such as agricultural or civil engineering machines, and other transport or handling vehicles.
The invention and its advantages will be readily understood in light of the description and the exemplary embodiments that follow, and also from the single FIGURE relating to these examples which schematically shows, in radial cross section, a pneumatic tire in accordance with one subject of the invention.